Semi-automatic telephone system.



BID. WlLLIS.

SEMI-AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED OCT. 1'; 1913.

Patnted June 19, 1917," 1

2 SHEETS-SHEET 1.,

@Mwm B. 0 WILLIS.

SEMI-AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED OCT. 7. I913.

41,230,639. ate1 1 tedJune19,1917.

In I Q IIIIIIIII IIH flTTOR/YEKS,

BERNARD n. wrnms or CHICAGO, rumors, Assrenon TOE-AUTOMATIC Emma COMPANY, or orrrcnso, ILLINOIS, A coRP'onA'rIoN OF ILLINOIS.

SEMI-AUTOMATIC TELEPHONE- sYs'rEM. I

To all whom it may concern:

Be it known that I, BERNARD a citizen of the United States of America, J

and resident of Chicago, Cook county, Illinois,

which the B-operator, upon receiving the busy signal, transmits a second busy signal to the A-operator to thus inform the l latter operator that the line is busy.

' thus giving to the A-operator the busy sig More speclfically, my invention relates to the means by which the B-operator, upon receiving the busy signal from the automatic apparatus through which the connection'to the called line was completed, operates a push-button or key switch, the operationof which causes a visual signal at the A-operators position to be intermittently operated,

nal.

My invention will be more readily understood by reference to the accompanying drawings, in which I-have illustrated my invention in connection with a semi-auto-' matic system of a particular type. Inthis system I have indicated a welLknown A -operators cord circuitwhich makes connection with a trunk -line in which is located the B- operators apparatus, the connection from this trunk being extended to the called line through an automatic connector switch of a well-known type.

It will, of course, be underst'ood'that other forms of cord circuits could be used, and likewise that in larger exchanges, instead of having the trunk line extending directly to the connector switch, a suitable number of selectors might be interposed in the well- In order to simplify the known manner. disclosure in this case, however, it isnot thought necessary to illustrate such selectors, as their use and the manner in which they aer connected are well ln iown.

Figs. 1 and 2 taken together show a complete circuit connection established between a calling manual substation T and a called automatic substation A. Fig. 1 shows the have invented certain new and useful I Improvements ,in Semi- Automatic Telesphone Systems, of'which the following is a Application filed October 7, 1913, Serial No. 793,947.

Specification ofLettcrs Patent. 1'9, 1917i p w manua l substation T. andan A- operators D. W1LL1s,-...

cord circuit S and a B operators equipment I. ;Fig. 2 shows an automatic connector and an automatic substation The'manual substation T .switch H, an individual or line switch C (Fig. 1) is an 'ordina ry common battery manual telephone comprising the usual" receiver 2, transmitter 3, ringer5 and "condenser 6. IMAt-the central ofiice the line of the substation T is provided with the usual answering 'jack J, a plurality ofmultiple jacks J ,"line relay 7 line lamp.-

8 and cut-01f relay 9. The cord'circuit S is a liven-known type of cord circuit comprising the- 'usualjanswering and calling plugs -P andP', respectively, inductively,

connected together through thefmedium of a repeating coil R. The usual supervisory relays 10 'and 11 are included in the sides of the cord circuit for controlling the supervisory lamps .12 and 13. The trunk circuit leading from the manual exchange to the automatic exchange leads from the multiple jacks J 2 on thifApperators board to a connectorswitch and is provided at the B-operators board in the automatic exchange,

with the equipment I. This trunking equipment comprises a lamp 14, a supervisory lamp 15, relays for-controlling the circuits of the lamps, keyS'K and K and the polarized r'elay 116. These two keys K and K are i so arranged that the operationof the key K- automatically restores the key K to normal position if the latter is in operated position at the time. The key K is a calling device key, the purpose of which is to connect acalling device with the trunk line, through the medium of which calling device the op erator may control the automatic switches to set up the proper connection. This calling device may be of any desired'type, such, for instance, as that shown in British patent 'to :S. G. S. Dicker No. 29,654 of 1.910. Through the medium of this calling device the operator may interrupt the bridge across the trunk line a desired number of times for each of the digits of the number of the called subscriber. v

' The, connector switch H (Fig. 2) is of the general type of connector switch disclosed in United States Letters Patent No.

815,176, issued March 13, 1906, to Keith,

Erickson and Erickson, the circuits, however, being modified to adapt the switch to operate in a system in which the central called line is controlled.

2 office apparatus is controlled by impulses transmitted over the tWo sides of the'line", in series. The connector is provided with a shaft (not shown) carryingwthe wipers 41, 42 and- 13 and is controlled by the vertical magnet 44 and the rotary magnet 45., The usual side switch carrying the wipers 16, 47, 48 and 19 is controlled by the private magnet 50 in the usual and well known -manner. The magnet 53 is the usual release magnet. The line relay '51 is connected With the line through the reversing springs of a so-called back-bridge relay 52, through the windings of which latterrelaythe called line is provided with talking current. The ringer relay 5 1 is the means through which the application of ringing current to the At Q there is shown a busy signaling machine "which is connected to the springs of the relay 55, the'function of which machine is to send a busy tone,- under certain conditions, back over the line. The complete operation ofthis relaywill be described "later. The busy signaling machine as represented herein comprises an 1nduct1on coil or transformer,

the primary windingof which isincluded in a local circuit with a battery and an interrupter. "Through the medium of this introlling automatic switches. Since the type of automatic substation shown at A andi the line switch C are well knownin the art of telephony, and as they form nopart of my present invention, it is thought unnecessary to give a detailed description of them.

For the purpose of supplying current for operating the centraloflice apparatus and for talking batteries B and B are shown having their positive terminals grounded at G and G. In practice, however, only one I battery need be used.

Having given a general description of the apparatus, I will now describe the opera. tions performed in the process of establishing a connection from the manual substation T (Fig. 1) to the automatic substation A (Fig. 2). Since theautomatic apparatus represented herein is in general well known'in the art, and is fully described in the publications herein referred to, its oper- 'ation will be described in a more or less general manner. Upon the removal of the receiven at the calling telephone T, the cir- -to prevent 1t f-romglowmg.

cuit of the line relay 7 is closed in the usual manner, which relay, upon energizing,

" closes the circuit of the line lamp 8 to signal the operator. The operator answers the call by inserting the plug]? into the jack J, whereby the'connection is completed between the line and the cord S. By the enga ement of the third conductor of the plug the jack J, the circuit of the cut-ofi'relay 9 is .closed in series With the lamp. 12 of the cord. The relay 9, upon energizing, disconnects the line relay from the line. When the connection is extended to the cord, the

calling substation is provided with talking current from the battery B throu h two windings of the induction coilit and through the relay 10. The relay 10, upon energizing, closes a shunt around the lamp.

12 through the resistance 60, thereby shunts mg suflicient current away from'said lamp The operator then connects her talking set with the line through the medium of the key K and,

upon learning from 'the calling subscriber that a subscriber of the automatic exchange 18 Wanted, she transmits the number to the B-op erator'over the usual order Wire. The

B-operator, uponreceiving the number, assigns to the A-operator an idle trunk'line, Which We Will assume to be the one terminating in the jack J Upon the insertion of the plug P into'the jack J a circuit is closed from ground G. over the tip strand through the plug P, jack J relay. 61, re-

lay 62, thence through the ring conductor of the jack J 2 and plug P and the'relay llto the non-grounded terminal of battery B. The relay 61- is of sufiicientlyhigh resistance to prevent sufficient current from flowing over this circuit to energize the relay 62 or the relay. 11, but is itself energized to close a circuit from ground G through contact of the'springs 63, back contact of the spring 64 and lamp'15 to battery B. The relay 61, upon energizlng, also operates to close a bridge across the trunk conductors 66 and 67, whereby .a circuit is closed extending from ground Gr through thelower Winding of the line relay 51'0f the connector H. thence through the springs 68 and 69, trunk conductor 67, springs 7 0 and 71 of the key K, polarized relay 16,.contac't 72 of the high resistance relay 61, sgrings 73 and 74c, conductor 6.6, springs 12 and 128 and the upper Winding of the relay 51 to battery. The direction of the flow of current overthis .circuit is such that the polarized relay does not operatively energize. The line relay 51,

howevenattracts its armature and closes acircuit extending from ground G through .the winding of .sloW acting release relay 100 to battery. The release relay,upon energizing, prepares the usual circuit for the vertical and rotary magnets 44 and 45, and also connects ground Gr to conductor 99. This latteroperation is unnecessary in .the system shown; in fact, where connectors only are used the connector 99 and springs 102 might "well be omitted. But in a larger system where selectors are used these parts are necessary for completing the usual holding circuit to prevent the release of the selectors included in the connection. v

The B-operator, upon learning the number of the desired station, operates the key K, whereby the polarized relay 16 is disconnected from the trunk and the calling device and ojierators set are bridged across same instead. The springs of the key are make, before break contacts, as shown in the drawings. An additional result of the operation of the key K is the closure of a circuit extending from ground G through the relay 65 to battery B. Upon energizing relay 65 looks itself at its left armature and at its right armatutre shifts ground G from lamp 15 to lamp 14, whereby the former is extinguished and the latter illuminated The operator now operates her calling device for the first digit'2 of the. called number, whereby the impulse springs 17 and 18 are operated twice momentarily, each time breaking the circuit of the connector line relay 51.

Since the relay 100 is slow acting it does not denergize during the momentary interruptions of. its circuit by the relay 51, so that each' time the latter relay is denergized a circuit is closed extending from ground G through the spring 108 and its back contact, spring 109 and its front contact, relay 110, vertical magnet 44 and the side switch wiper 49 to battery B. The vertical magnet 44 receives two impulses over this circuit and operates to raise the switch wipers 41, 42 and 43 to a position opposite the second level of bank contacts. The relay 110, which is included in series with-the' vertical magnet, remains in its energized position during the entire time impulses are being transmitted through it and operates to close the circuit of the private magnet 50. After, the

last impulse is delivered, the relay 110 opens thecircuit of the private magnet 50, which,

wipers are rotated onto the contacts of the desired line. The relay110 operates in response to the impulses for this digit in the same manner as for the previous digits, to cause the private magnet 50 to advance the side switch one more position-that is, from second to third position. By the engagement of the side switch Wipers 46 and 47 with their third-position contact points, the line connection is finally completed with the called substation, as shown by the heavy conductors. The circuit of the cut-off winding of the called subscribers line switch is closed by the side switch wiper 48 passing to third position, said circuit extending from ground. G through the side switch wiper 48, private wiper 43 and through the winding 108 to battery. The connection. of

ground G with the connector private bank contact of the called line over a portion of the circuit just traced provides said contact and its multiples with'a guarding potential to prevent the busy linefrom beingv seized by any other connector switch. By the engagement of the side switch wiper 49 with its third-position contact point, the circuit of the ringing relay 54 is closed, which circuit extends from ground G through: the

interrupter 109, relay 54, springs 110 and the side switch wiper 49 to battery B. The

ringing relay 54, upon energizing, 'disconnects the calling line from the called line and bridges the ringing current generator 111 across the called line to signal the called subscriber. The ringing relay is energized only intermittently through the medium of the interrupter 109*. The B-operator, upon completingthe call, restores the key K to normal position, thereby disconnecting the calling device and again placing the polar ized relay 16 across the trunk lines 66 and 67 and disconnecting ground G from the relay 65. Upon the/response of the called subscriber his line is provided with talking current through the windings of'the backbridge relay 52 of the connector switch, which relay,upon energizing, closes the circuit of the ringing-cutoff relay 112, said.

circuit extending from battery B through the relay 112, springs 113 and 114 and the wiper 48 to ground G The relay 112, upon energizing, interrupts the circuit of the ringing relay 54 at the springs 110 and closes a locking circuit for itself through its own springs 115 and 116, independent of the springs of the back-bridge relay 52. A further result of the energization of the relay '52 upon the response of the called subscriberis the transportation of the connection between the windings of the line relay 51 and the trunk conductors 66 and 67, whereby the direction of current in the trunks 66 and 67 is reversed. This reversal of current in the trunks 66 and 67 causes the polarized relay.

16- to operatively energize. The relay 16,

upon energizing, puts a short-circuit around v the high resistance relay 61. This shortcircuiting of the relay 61 allows the relays 62 and 11 to operatively energize and the relay 61 deenergizes. The energization of the relay 62 supplies a new holding ground for the relay 65 and also, by ,closin the springs 117, prevents the relay 16 from be disconnected from the trunks when the re busy, and itwill also-be explained how the 'A-operator receives the so-called flash busy signal, whereby she is'also informed that the i 'called line is busy. Referring now to the.

lay '61falls back. The energization of the relay 11 of the A-operators cord circuit short-circuits'the lamp 13 by means of theresistance 118, whereby the lamp 13 is extinguished. This operation informs the A- operator that the called subscriber has answered.\ a

, After the conversation is completed the I operator. is given the release signal in the-following manner: The hanging up of the re' ceiver at the calling substation allows the relay 10 to deenergize, which operation reconnector H (Fig. 2), if the called line is a busy the private bank contactupon'which 7 --the private wiper 43 comes to rest will be supplied with a guarding ground potential,

' relay 55.

moves the short-circuit from the disconnect lamp :12. The hanging up of the receiver at the*called substation breaks the energizing circuitfor the relay 52 ofthe connector.

The relay 52, upon denergizing, again re-l verses the current in the trunks 66 and 67, which again allows the relay 16 to fall back; and disconnect .theshunt from the relay 61. The relay 61", upon again being placed'in the:

circuit, causes the relays 62 and 11"to fall back. Therelay 11, upon falling back, dis- "connects the shert-circuit from around the lamp l3, whereupon' 'the lamp will glow.

Thus the simultaneous glowing of the lamps 12 and 13 informs the A-operator that the p, moves the plugs P and P from their respective-jacks.- The removal of the plug P from its jack clears the cut-off relay 9 and lamp 12 in the usual and-well-known man ner. The removal of the plug P from its jack breaks the circuit of the relays 61 and 62, which, upon deenergizing, break the looking circuit of relay 65 and also open the lay 55, upon energizing,- opens the circuit of the rotary magnet,closes a locking circuit either by reason of having calledor having been called, in the usual and well-known" 75 manner. The wiper43, upon comingin contact with this guarding ground'an'd before the side switch has passed to thirdposition, 'will close a circuit through thebusy locking This circuitv extends from said ground at the private wiper 43 through the wiper 48 (in second position), springs 121 and 122, relay 55, springs .123 and 1-24 and the private magn'et to battery B. The refor "itself in series-with the ,privatemagnet and also-puts a busy signal .on thej'oalling line, said circuit extending from the busy machine o through thespring :90

wiper' e'i, thence over the-heavycoiiductor -67 to'and throughtheB-operators set L.

:back over the; heavy conductor .66 to an conversationyis completed. She then re ting the busy signal to be transmitted to and bridge across the conductors" 66 and 67, whereby the circuit of the line relay '51 of the connector is broken. The line relay 51, upon deenergizing, opens the circuit of the relay 100, which in turn falls back, thereby closing a circuit through the release 1 magnet 53..

The circuit. through the connector release back contact of the-spring-108 50 magnet extends from ground G through the back contact of the'spring 109, off normal springs 120 and release magnet 53 to battery B. The

magnet 53, upon energizing, operates to re-.

store the shaft and side switch to normal position. Its own circuit is broken at the,

ofi'-normali springs 120 when the shaft reaches its lowest position. Thus it 'Wlll be seen that all of. the apparatus is returned to normal position and is in readiness for another call.

It having been explained how connection may be completed with an automatic line through the medium of an A-operator and a B-operatorwhensaid line is idle, 1t W111 now be explained how said connection canbe prevented from bei-ng made if the called llne is 'K closesthe circuit of the relay relay 61 extends from ground G" through gized in this manner, operates to flash the through the connector back-bridge relay t springs 127 and 128 and the upper winding of the relay 51 to battery. Upon the B'-op 'erator receiving the busy signal she presses a the key K, which operation automatically restores the key K to normal positiomthus closing the talking conductors andperm'itthrough the calling subscriberifs receiver, v thereby informing him that the called fine is in use. He then replaces the receiver on the o Ying t e n-o'perator the'usual disconnect signal. The depressing of the keythe interrupter 136, springs 13'?- and 138, thence through the-relay 61, plug P and the. jack J? to ground G". The relay 11, upon being intermittently energized and deener- 125 lamp 13, thereby informing the operator that the called lin'e is' busy. If the calling subscriber does not hang up his receiver immediately after hearing the busy signal, the A-operator, upon receiving the'busy signal, 139

129. This 6' may inform the calling subscriber that the forms of cord circuits and automatic apparatus may be employed Without departing from the spirit of my invention.

What I claim as my invention is 1. Ina telephone system, a called line, an

A-operators board, a B-operators board,

from saidautomatic switches attempt tomake' connection with a busy linef I 2. In a telephone system, a called line, an A-operators board, a B-operators board, automatic switches for extending connection from said B-operators board to the called line, a visual signal on said A-operators board, and automatic means controlled by said B- operator for intermittently operating said signal when said automatic switches attempt to make connection with a busy line.

In a telephone system, acalledline, an A-operators board, a B-operators board,

' automatic switches, means for extending connection from sald B-operators board to said switches, means for controlling said switches for extending connection to sa1 called line, a. signal at said A-operators 1 board, a relay bridged across. the conductors of the talking circuit at said B-operators board, means controlled by said B-operator V for extending connection to the called line,

1 signal.

for intermittently varying the resistance of said bridge when said. automatic switches attempt to make connection with busy line, 1 and means controlled by' the variation of said .current for intermittently operating said 4. In a automatic. switches, means for extending connectlon from said A-operators board to said B-operators board and from said B- operators board to said automatic switches, means controlled by said automatic switches a signal on said A-operators board, a bridge across the conductors of the talkingcircuit,

means controlled by said B-op'erator for-in; A

':tion of; said. signal at] said A-operat'o'rs board '1 v 1 f l v I 9. 'In' a telephone system, a called line, an

creasing the fiow of current through said bridge when said automatic switches attempt 1 to lmake connection with a busy line, and means controlled by said increased flow of current for operating said signal.

automatic switches, means for I haveillustrated and described one automatic swltches for extending connection. B-operators board to the called line, a signal on said A-operators board and automatic -means controlled by said B-operator to operate said signal when said telephone system,,a called line, an A-operators board, a B-operators'board,

5 In a telephonesystein, a called line, an

A-operators board, a B-operators board,

extending connection from said A-operators board to said 'B-operators board and from said B- operators board to said automatic switches, means controlled by said automatic switches for extending connection to the called line,

across the conductors of the talking circuit,

"a signal on said A-operators board,.a bridge means controlled by said B-operator for-inswitches attemptto make connection with operating signal.

6.v In atelephone system, a called line, an A-operators board, a B-operators board,

autbmatic-switfches controlled from said 3- operatorsboard iior extending connection termittently increasing the flow of current 1 vthrough-said bridge when said automatic to the called line, a signal on said A-oper-;

ators board, a relay;controlling said signal,

a circuit for said relay, and means controlled by said-'B-operator for intermittently varying' the resistance of said circuit to thereby. intermittently operate'said signal. 7. In a telephone system, a called line, an. A-operators board, a B-operators board, automatic switches controlled from said-B- to the called line, a signal on said A-oper-- operators board for extending connection ators board, a relay controlling said signal,

a high resistance bridge .across theconduc- I u l I tors board, a circuit fOnSaJd relay includtors ofthe talking circuit at 'said B-operaing said bridge, means for transmittingfla tion with the busy line, and mea'ns con 8.;In fa telephone'sys'tem, called line, an A-operators board, a B-operators board,

ductors of the I talking circuit atsaid operators" board, a circuit for-said? relay 'in-- "eluding J saidbridge, means 'for. .transmitting a'bus'y signal to the B-ioperatorwhen said automatic switches attempt to make (3011- busy signal to the Be'operator when-said au-P d -tomat1c switches attempt to makerconnecautomatic switchescontrolled from said 'B- "operatlorls board 'for extending connection (to the called line, a signal onr'said A-oper- 'ators board, a relay, controlling said sig, "nal; a'highresistance bridge acrossthe c'o'n- 'nectionwithithe busy line, and means "controlled by said B-operator for intermittently decreasing the resistanceflof said relay circuit to therebymuse theinter'mittent: opera-Y operators board. for extending connection .to' the called line, a signal on said A-operators board, a relay controlling said signal, a high resistance bridge across the conductors of the talking circuit at said- B-operators board, a circuit for said relay including said bridge, means for transmitting aibusy signal to the B-operator when said antomatic switches attempt to make connection with the-busy line, a relay associated with -;said B-operators board, means controlled by said Bsoperator for energizing said relay, and means controlled by the energization of said relay for reducing the resistance of said relay circuit to thereby cause the operation of said signal at said A-operators board.

10. In a telephone system, a called line, an A-operators board, a B-operators board, automatic switches controlled from said B- v operators board for extending connection to the called line, a signal on said A-operators board, a relay controlling saidsignal, a high resistance bridge across the bonductorsof the talking circuit at said B-operators board, a circuit for said relay including said bridge, means for transmitting a busy signal to the B-op'erator when said automatic switches attemptto make connection with the busy line, arelay associated with said B-operators board, means controlled by said. B-operator for-energizing said relay,

a locking circuit for said relay for maintaining said relay energized,'and means controlled by the energization of said relay for '35: reducing the resistancev of said relay circuit to thereby cause the operation of said signal at said A-operators board. c

11. In a telephone system, acalled line,

an A-operators board, a B-operators board,

0' automatic switches, means for extending connection from said B-operators board to said switches, means for controlling said switches for extending, connection to said" called line, a signal at said A-operators board, a pair of relays b'ridgedacross the conductors of the talking circuit at said B- operators board, means controlled by said B-operator for connecting ground to said bridge at a point between saidrelays, and

means controlled by said ground connection for operating said signal at said A-operators board. s 12. In a telephone system, a called line,

an A-operators board, a B-operators board,

automatic switches, means for extending connection from said B-operators board to said switches, means for controlling said switches for extending connection to said called line, a'signal at said A-operators board, a pair of 80 relays bridged across the conductors of the talking circuit at said -B-operators board, means controlled by said B-operator for in termittently connecting ground to said bridge at a point between said relay, and

means controlled by said intermittent called line, a signal at said A-operators board, a pair ,of relays bridged across the 'connectionfor operating said signal at said nection from said B-operators board to said connection for intermittently operating said ground connectionfor intermittently operating said signalat said A-operators board., 13. In a telephone system, a called line, an

-A-operators board, a Bsoperators board,

automatic switches, means for extending connection from said B-operators board to said switches, means for controlling said switches for extending connection to said I 5 conductors of the talking circuit at said B4 operators board, a third relay associated with said B-operat01"s' board, means controlled by said B-operator for energlzing said third relay, -means controlled by the energization of said third relay for establishinga ground connection to said bridge at a point between said first-mentioned relays, and means controlledby said ground r A-operators board.

14;. In atelephone system, a called line, an A-operators board, a B-operators board, automatic switches, means for extending conswitches, means for controlling said switches for extending connection to said called line,

a signal at said A-op'erators board, a pair of relays bridged across the conductors of the' talking circuit at said B-dperators board, a thirdrelay associated with said B-oper ators board, means controlled by said B operator, for energizing said third relay, means controlled by the energization of said third relay for establishing an intermittent 00 ground connection to said bridge at a point between] said' first-mentionedrelays, and means controlled by saidintermittent ground signal at said A-operators board. I

15. In a telephone system, acalled line, an A-operators board, a B-operators board, automatic switches, means for extending connection from said B'-operator?s board to Said switches, means for controlling said switches for extending connection tosaid called line, a signal at said A-operators board, a pair of relays bridged across the.

.. conductors of the talking circuit at said B- operators board, a third relay associated with said B-operators board, means controlled by said B-operator for energizingsaid third relay, means controlled by the energization of said third relay for establishing an intermittent ground connection to said bridge at a point between said firstmentioned relays, means.controlled by said intermittent ground connection for intermittentlv operating said signal at'said A operators board, and a locking circuit for said third relay for maintaining the same energized. 16. In a telephone system, a calling and a called subscribers line, an A-operators cord circuit adapted to be connected with the call line,

a B-operators set adapted to be bridged across said'trunkby the operation of said listening key, automatic switches for-extending connection line, means for transmitting a busy signal backto said B-operators board when an j attempt is made to establish connection with a busy line, a busy button associated with said B-operators board, and means controlled by the operation of said button for I transmitting a busy signal back to the A to the calling line. Y I p 17. In a telephone system, a plurality of #subscribers lines, meansincluding an A operators Icord circuit and a B-operators A cord circuit for establishing connection between two of said lines, means for automatieally testing the called line, means whereby operator and for releasing said listening key 15 to thereby permitthe usy signal to be transmitted over the talking conductors back from said trunk to the called the B-operator receives a busy signal imine- -diately upon establishing connection with a busy line, and means controlled by said B-operator for then transmltting a busy signal to the A-operator,

18. In a telephone system, a plurality of subscribers lines,means including an A- operators, cord circuit, a B-operators cord circuit and automatic progressively movable switching apparatus for'establishing connection between two of said lines, means whereby the B-operator receives a busy signal immediately upon establishing connection with a' busy line, and means controlled'by said B-operato'r for then transmitting a busy sig-' nal tothe A-operator.

\ Signed by me at Chicago, Cook county, Illinois, this 29th dayoof September, 1913. y BERNARD D. WILLIS.

Witnesses: u

- G. YANooHowsm,

H. E. HERSH Y, 

